QUESTION:

What are PCI-E 16x Slot?

ANSWER:

There are 2 of them on this motherrboard diagram, both are blue. These are for your grahpics card. With two of them onboard, you can run 2 graphic cards in SLI. You will only need this if you're a gamer, or working with high end video / grahpics editing. These are the 16x speed versions, which are currently the fastest.